JPH0311574Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a glow plug used for preheating the sub-combustion chamber or combustion chamber of a diesel engine, and particularly to a diesel engine using a ceramic heater as a heating element. Regarding the improvement of glow plugs for

[Conventional technology]

In general, diesel engines have poor startability at low temperatures, so a glow plug is installed in the auxiliary combustion chamber or combustion chamber, and by passing an electric current through it and generating heat, it is possible to raise the intake air temperature or use it as an ignition source. A method has been adopted to improve engine startability. In recent years, this type of glow plug has been developed, for example in Japanese Patent Laid-Open No. 57-41523, using a ceramic heater type heater that uses a rod-shaped heater in which a heating wire such as tungsten is embedded in an insulating ceramic material such as silicon nitride. Compared to the conventionally common sheath type, a new type has been proposed that improves heat transfer efficiency and has superior heat generation characteristics.Moreover, it becomes red hot in a short time when heated, greatly improving temperature rise characteristics. , is attracting attention because it can demonstrate its performance as a rapid heating type.

[Problem that the invention attempts to solve]

By the way, in the conventional ceramic heater type glow plug described above, in order to connect one end of the resistor buried in the ceramic heater to ground via the holder, the heater is held at the tip of the holder. Although it is common practice to use metal pipes, some problems have arisen in this case. In other words, since these ceramic heaters and metal pipes have different coefficients of thermal expansion, when the heater generates heat or when the metal pipe that holds the heater is brazed with the holder, the difference between the two may occur. Brazing can cause the joints to separate and create gaps, which can cause the brazed parts to peel off, resulting in not only poor electrical connections, but also problems such as not being able to maintain mechanical strength. There is a
It was no longer able to function as a glow plug.

To explain this in detail, in this type of glow plug, the tip of the heater heats up to a considerable temperature when it generates heat, and due to the influence of heat, the metal pipe and metal holder that hold the heater are stronger than ceramic heaters. is also greatly thermally expanded,
As a result, the inner circumference of the metal pipe, which also serves as an electrical connection, separates from the outer circumference of the heater, creating a gap.
There was a risk that the brazed part would peel off and cause poor contact. Further, a similar problem occurs due to the effect of heat when brazing the metal pipe that holds the heater to the holder.

Furthermore, in the conventional glow plug described above, the ground side lead end of the resistor buried in the ceramic heater is exposed at the part where the metal pipe is silver-brazed. If there is a gap between the heater and the metal pipe, moisture will enter from the outside through capillary action, making it impossible to maintain the joint strength and conductivity of this area, as well as damaging the resistor buried inside the heater. For,
There is also a risk that the lead end may enter the heater through the resistor, resulting in deterioration of its performance. In other words, as mentioned above, if the heater is energized to rapidly heat it with moisture infiltrating the heater, the moisture inside the heater will vaporize and expand, causing damage to the heater. There was a risk of being invited. For this reason, the present applicant has previously proposed, in accordance with Japanese Utility Model Application Publication No. 60-12063, etc., to expose one end of the resistor at a portion near the rear end of the heater rod facing into the holder, and to expose a cross section of the heater rod at this portion. A configuration in which a terminal ring formed to match the shape is fitted and a part of it is connected to the inner end of the metal pipe that holds the heater rod at the tip of the holder using a connecting piece or lead. We are proposing something based on However, in such a configuration, the processing of the terminal ring to be fitted onto the heater rod in a state where electrical connection is possible is not only troublesome and complicated due to the cross-sectional shape of the heater rod, but also the processing of the terminal ring is difficult due to the cross-sectional shape of the heater rod. The connection to the metal pipe side is a point contact using a connecting piece or the tip of a lead, which leads to practical problems such as a lack of reliability in electrical connection and the troublesome connection work. Taking these points into consideration, it is necessary to take some measures that can eliminate the above-mentioned problems.

[Means for solving problems]

The diesel engine glow plug according to the present invention has one end of the resistor embedded in the bar-shaped ceramic heater held at the tip of the holder via the metal pipe, and one end of the resistor embedded in the rod-shaped ceramic heater that is held at the tip of the holder through the metal pipe. A grip part is exposed on the outer peripheral part near the end and is curved and wrapped around the exposed part in at least two places in the circumferential direction, and the grip part is connected to the grip part via an arm part and is inside the metal pipe. A metal thin plate consisting of a base end formed in a substantially disk shape so as to be joined in surface contact with both ends, and a base end having an inner hole in the center thereof through which a heater is loosely fitted. This is provided with an electrode fitting that is bent and formed.

[Effect]

According to the present invention, the end of the resistor lead in the ceramic heater is shifted and exposed inside the holder where the heat effect is smaller than the joint part with the metal pipe, and this exposed part is firmly attached to the inner end of the metal pipe. Because the connection is securely gripped by the gripping part of the electrode fitting that is bonded and fixed to the metal pipe, there are no problems with electrical and mechanical connections caused by the difference in thermal expansion coefficient between the conventional metal pipe and ceramic heater. In addition, the electrode fitting can be easily and inexpensively formed by press-forming a thin metal plate, and is excellent in terms of mass production.

〔Example〕

Hereinafter, the present invention will be explained in detail using embodiments shown in the drawings.

Figures 1 to 5 show an embodiment of a glow plug for a diesel engine according to the present invention.
The schematic structure of the diesel engine glow plug shown in FIG. 5 will be briefly explained using FIG. 5. This glow plug 1 includes a resistor (indicated by reference numeral 10 in FIG. 1) whose tip side functions as a heating element when energized.
and a pair of lead bodies (11a, 11b in Fig. 1), which are other resistors connected to both ends, are embedded inside the bar-shaped ceramic rod made entirely of a heat-resistant and insulating ceramic material. It comprises a heater 2 and a metal holder 3 having a substantially tubular shape that holds the ceramic heater 2 at its tip,
An external connection terminal 5 is fitted concentrically to the rear end of the holder 3 via an insulating bushing 4 made of synthetic resin, etc., and this external connection terminal 5 extends from the rear end of the heater 2. A metal conducting wire 6 such as a flexible wire is connected to the tip by spot welding or the like.

Here, as is well known, the above-mentioned ceramic heater 2 has a substantially elliptical cross section, and is produced by pressurizing and firing ceramic powder filled with the above-mentioned resistors 10, 11a, 11b held in a mold. In this case, the cross section is made into a substantially elliptical shape in order to improve the density of the ceramic material compared to a circular shape, and to make the heat resistance strength, thermal conductivity, etc. more effective. The ceramic heater 2 is made of silicon, a so-called fine ceramic material that is stable in performance even in high-temperature conditions (up to about 1700 degrees Celsius) and has excellent insulation and thermal shock resistance. Non-oxides such as
For example, silicon-based nitride is preferable.

Further, in the figure, 2a, 2b, and 2c are metal coating layers formed on the outer periphery of the central portion in the axial direction, the outer periphery of the rear end portion, the outer periphery of the rear end portion, and the end face, respectively. The metal coating layers 2b and 2c at two places on the rear end side are attached to the pair of lead bodies 11a and 1 at both ends of the resistor buried in the heater 2, respectively.
1b. That is, since the above-mentioned ceramic heater 2 generally causes some problems when bonded to metal materials, the above-mentioned metal coating layers 2a, 2b, and 2c are formed on the surface of the ceramic material in advance to improve the adhesion with the metal material. This ensures that the joint strength is reliable. A reinforcing metal pipe 7 fitted and fixed to the outer periphery of the metal coating layer 2a at the center of the heater 2 is connected to the metal coating layer 2a, and is connected to the holder 3 side through this. Further, the metal coating layer 2b near the rear end is connected to the metal pipe 7 side by being gripped by the grip part 21 of the electrode fitting 20, which will be described later, and is joined to the inner end of the metal pipe 7. A terminal cap 8 is placed on the end side 2c and connected to the conductive wire 6. In this case, the metal pipe 7 is connected to the heater 2
This serves as a reinforcing member to hold the heater 2 at the tip of the holder 3, and the through hole inside the heater 2
The heater 2 and the holder 3 are each fixed to the heater 2 and the holder 3 by silver brazing or the like. Further, the terminal cap 8 is similarly formed to match the cross-sectional shape of the heater 2, and is fixed by silver brazing or the like with the conductive wire 6 connected by welding or the like.

The threaded portion formed on the rear end side of the external connection terminal 5 includes an insulating ring 9a, a fixing nut 9b, a spring washer 9c, and a washer 9.
d, and a nut 9e for tightening the external lead is screwed together, and the external connection terminal is connected by sandwiching the lead wire from the battery (not shown) between the washer 9d and the nut 9e and tightening the nut 9e. 5 is electrically connected to the battery terminal. By screwing the threaded portion 3a formed on the outer periphery of the holder 3 into a threaded hole formed in the cylinder head of the engine, the resistor in the ceramic heater 2 is electrically connected via the holder 3. connected to ground. In addition, 4a in the figure is fitted onto the outer periphery of an insulating bushing 4 that holds an external connection terminal 5 at the rear end of the holder 3, and is buckled in the axial direction due to the high pressure applied by the rear end of the holder 3, which is caulked during assembly. This is a metal tube for integrating the insulating bushing 4 with the holder 3 side with the required mechanical strength and creating a structure that is less susceptible to temperature effects. Furthermore, the reason why the external connection terminal 5 is connected to the ceramic heater 2 described above using the metal conductor wire 6 is to strongly protect the heater 2 from mechanical external forces such as various vibrations and tightening torques applied to the external connection terminal 5. Therefore, it is preferable to use a material for the conducting wire 6 that has a certain degree of flexibility.

Now, according to the present invention, in the ceramic heater type glow plug 1 having the above-described configuration, one (earth side) lead body 11a of the rod-shaped ceramic heater 2 in which the resistors 10, 11a, and 11b are embedded is connected to a metal. The outer circumferential portion closer to the rear end than the central portion in the axial direction held by the manufactured pipe 7 is exposed and connected to the metal coating layer 2b, and this exposed portion (metal coating layer 2b) is connected to at least two locations in the circumferential direction. A grip part 21 is curved and wrapped around the grip part 21, and the grip part 21 is connected to the grip part 21 via an arm part 22, and is joined to the inner end 7a of the metal pipe 7 by silver brazing in surface contact. The base end portion 23 is formed into a substantially disk shape and has an inner hole portion 23a in the center thereof through which the heater 2 is loosely fitted.
It is characterized by the provision of an electrode fitting 20 formed by bending a press-formed thin metal plate (see FIGS. 3 and 4).

That is, according to the present invention, the conventional heater 2
When the heater 2 is grounded to the holder 3 using the metal pipe 7 that holds the central part of the metal pipe 7, the metal pipe 7 expands thermally, causing poor contact with the heater 2. In order to solve this problem, the heater 2 is moved so that the grounding part from the heater 2 is separated from the tip of the heater 2, which generates a large amount of self-heating, and also from the joint between the metal pipe 7 and the holder 3. 2, and is placed in an indirect connection state using an electrode fitting 20.

With such a configuration, when the heater 2 generates heat or during brazing heating when the metal pipe 7 fixed in advance to the heater 2 is assembled to the holder 3 side, the metal pipe 7 is heated due to the thermal influence. Even if the electrode metal 20 expands thermally, the thermal effect will not affect the electrode metal fitting 20, and the heater 2 of this electrode metal fitting 20 will not be affected by the thermal expansion.
The connection state between the grip portion 21 and the base end portion 2 of the metal fitting is also
This can be appropriately and reliably absorbed by the elastic displacement of the arm portion 22 that connects the heater 2.
The ground connection from the holder 3 to the holder 3 can be easily and appropriately performed. Furthermore, in such a configuration, since the exposed portion of the lead body 11a inside the heater 2 is not the metal pipe 7 portion, there is a risk that moisture may infiltrate into the heater 2 through the resistor as in the conventional case. The benefits are obvious.

As is clear from FIGS. 2 to 4, the electrode fitting 20 can be easily and easily formed by press-forming a thin metal plate entirely made of a conductive metal material and bending it into a desired state. The base end 23 is formed to match the shape of the end face of the metal pipe 7, and has an inner hole 23a through which the heater 2 is loosely fitted. A grip portion 21 is formed continuously from a portion of the periphery via an arm portion 22. The gripping portion 21 is curved and bent around the metal coating layer 2b formed on the outer peripheral portion near the rear end of the heater 2 to securely grip the heater 2. At least the conductive parts 21a and 21b at both ends are fixed by silver soldering to ensure electrical connection.

In addition, in the figure, reference numeral 24 denotes a caulked portion extending to the opposite side of the gripping portion 21 via the arm portion 25, and this caulking portion 24 is attached to the gripping portion 21 that grips the heater 2.
At least both end portions 21a and 21b of the curved portion 24 of both ends are overlapped from the outside.
a and 24b, and is configured to prevent deformation of the gripping portion 21 due to thermal effects when the electrode fitting 20 is silver soldered to the metal pipe 7 or the heater 2 side. In addition, 26 in the figure is the gripping portion 2.
1 is a guide protrusion that is bent and formed from the sides of the conductive parts 21a and 21b, and is used to easily and appropriately assemble the caulking part 24 to the grip part 21 when the electrode fitting 20 is attached. It is something.

Then, the electrode fitting 20 with such a configuration
simply press-forms a thin metal plate and bends it.
Although it is easy and properly formed and can ensure electrical connection, it has great practical advantages such as excellent mass production and low cost. . Further, according to the electrode fitting 20 made of such a thin metal plate, the heater 2
Since it is made of a thin plate material, the difference in thermal expansion with the heater 2 is small, and a reliable ground connection can be made.

Here, the reference numeral 27 in FIG. 1 is the heater 2 mentioned above.
The effect of providing such a sealing material 27, which is a sealing material such as silicone rubber applied to insulate the rear end portion, will be obvious.

It should be noted that the present invention is not limited to the structure of the embodiment described above, and the shape, structure, etc. of each part of the glow plug 1 may be modified and changed as appropriate, and various modifications are possible.

[Effect of idea]

As explained above, according to the glow plug for a diesel engine according to the present invention, one end of the resistor embedded in the rod-shaped ceramic heater held at the tip of the holder via a metal pipe is made of metal. A grip part is exposed on the outer peripheral part closer to the rear end than the part held by the pipe, and is curved and wrapped around the exposed part in at least two places in the circumferential direction, and the arm part is connected to the grip part. It is formed into a substantially disk shape so as to be connected to the inner end of the metal pipe in a surface contact state, and an inner hole portion is bored in the center portion thereof, through which the heater is loosely fitted. Since the electrode fitting is formed by bending a thin metal plate, the end of the resistor lead inside the ceramic heater can be easily connected to the metal pipe. The exposed part is shifted to the inside of the holder, which is less affected by heat than the conventional one, and this exposed part is securely gripped and connected by the grip of the electrode fitting, which is firmly fixed to the inner end of the metal pipe. In addition to being able to eliminate problems in electrical and mechanical connections caused by the difference in thermal expansion coefficient between metal pipes and ceramic heaters,
Electrode fittings are easily and inexpensively formed by press-molding thin metal plates, and have great practical effects, such as being excellent in terms of mass production.

[Brief explanation of the drawing]

Fig. 1 is an enlarged vertical sectional side view of the essential parts of an embodiment of a glow plug for a diesel engine according to the present invention, Fig. 2 is a schematic perspective view showing the configuration of the main parts, and Figs. 3 and 4 are the invention of the present invention. A developed view of the electrode fitting that characterizes this and a side view showing its usage condition, Part 5
The figure is a schematic longitudinal sectional side view of the entire glow plug for a diesel engine to which the present invention is applied. 1...Glow plug for diesel engine, 2
...Ceramic heater, 2a, 2b, 2c...Metal coating layer, 3...Hollow holder, 5...
External connection terminal, 6... Metal conductor wire, 7... Metal pipe, 8... Terminal cap, 10... Resistor, 11a, 11b... Lead body, 20... Electrode fitting, 21... Gripping part, 22 ...Arm part, 23...
Base end portion, 24... caulking portion, 27... sealing material.

Claims (1)

[Scope of utility model registration request] In a glow plug for a diesel engine, a rod-shaped ceramic heater having a resistor embedded therein is held in a hollow holder tip through a metal pipe fitted in the axial center of the rod-shaped ceramic heater. One end of the buried resistor is exposed at an outer peripheral portion closer to the rear end than the portion held by the metal pipe, and the exposed portion is curved and wrapped so as to be gripped at at least two points in the circumferential direction. The gripping portion is connected to the gripping portion via an arm portion, and is formed into a substantially disk shape so as to be joined to the inner end of the metal pipe in surface contact, and the heater is attached to the center portion of the gripping portion. 1. A glow plug for a diesel engine, comprising an electrode fitting formed by bending a thin metal plate, the base end having an inner hole through which the glow plug loosely fits.